The present invention relates to a pressure/stroke controlled injector with a hydraulic convertor or multiplier.
In fuel injection systems for injection of fuel in combustion chambers of internal combustion engines nowadays electrically controlled injectors are utilized. Injection start and injection end are adjusted with them. The injectors are mounted preferably by clamping devices on a cylinder head of an internal combustion engine. Thereby injectors which are loaded via a high pressure collecting chamber (common rail) can be mounted on the cylinder head of the internal combustion engines without substantial changes.
German patent document DE 198 235 494 discloses a pump-nozzle unit which operates for the fuel supply in combustion chambers of direct-injection internal combustion engines. For providing a pump-nozzle unit, which has a simple construction, a small size and in particular a short response time it is proposed to form the valve actuator as a piezo electric actuator.
The pump-nozzle unit disclosed in this document has a hydraulic convertor or multiplier device which performs various functions. First, it represents a rigid connection between the valve actuating unit and the control valve and ensures therefore a secure and reliable transmission of the expansion movement of the piezo-electric actuator to the A-valve. Moreover, the expansion movement of the valve actuating unit is deviated by the hydraulic multiplier device into a differently directed valve actuating movement. In the shown example the downwardly oriented expansion movement of the piezo-electric actuator is converted into an upwardly oriented valve actuating movement, or in other words the valve actuating movement oriented in an opposite direction. Moreover, by a respective selection of the surfaces of the valve actuating unit which cooperate with the hydraulic multiplier device on the one hand and the control valve on the other hand, a desired multiplication ratio between the expansion movement of the piezo-electric actuator and the valve actuating movement is provided. Relatively small expansion movements of the piezo-electric actuator can be converted into relatively great valve actuating movements.
Finally, the hydraulic multiplier device serves also as a thermal compensation element between the valve actuating unit and the control valve. In this function, the hydraulic multiplier device compensates the action of various temperature coefficients of the piezo-electric actuator on the one hand and the A valve on the other hand.
Accordingly, it is an object of present invention to provide a pressure/stroke controlled injector which avoids the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a pressure/stroke controlled injector which is actuatable by a single control element.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a combustion chamber of an internal combustion engine, comprising an injector housing; 2/2-way double valves received in said injector housing and coupled with one another for joint vertical movements; a hydraulic multiplier associated with said 2/2-way-control valves; a nozzle chamber which surrounds a nozzle needle and supplied with high pressure fuel by said hydraulic multiplier, said 2/2-way control valves in said housing being turned relative to one another and have valve bodies and guiding elements which surround said valve bodies.
With the proposed solution, a hydraulic multiplier is realized, which is completely forced-compensated, so that the utilized control element must apply small control forces for providing an actuation of the parallel connected 2/2-way control valves. When however such low control forces are required, the inventive injector can be connected with a magnet. With magnets as actuating units, a lasting operation of the injector over the service life of the fuel injection system is ensured.
The force compensation unit of the 2/2-way valves with the hydraulic multiplier is provided by the turning relative to one another with respect to their opening direction. For obtaining the force compensation in the valve body of the 2/2-way valves, the both valve bodies are formed symmetrically, but turned relative to one another. The valve bodies which are movable in the housing of the injector in the vertical direction up and down have a first diameter, while guiding sleeves are received on them and have a second diameter which exceeds the first diameter. The guiding sleeves which have the second diameter are provided with ring-shaped abutment surfaces which limit the maximum vertical covered path of the valve body. Each valve body which operates as the 2/2-way valve is loaded with a spring element which, with the complete force compensation unit of the valve, applies the force to be overcome by the actuating unit.
An overflow connection between both valve chambers is provided between the both parallel actuated, pressure-compensated 2/2-way control valves. An inlet to a hydraulic multiplier branches from the above mentioned overflow connection. It fills the nozzle chamber which surrounds an injection nozzle in the region of a pressure stage, with fuel under high pressure. A closing piston is formed on the nozzle needle and cooperates with a control chamber volume enclosed in a control chamber. The pressure release in the control chamber leads to an outside movement of the nozzle needle from its seat and thereby to a release of the injection openings in the combustion chamber of the internal combustion engine. The control chamber in turn can be pressure loaded with an outlet nozzle released by an actuator.
The parallel connection of the 2/2-way control valve allows a control of the valve body so that during a release of the sealing seat one seat of one of the valve bodies of the 2/2-way control valve, the other moves to its sealing seat and vice versa.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.